Test of various clock implementations -- https://martin-ueding.de/posts/clock-test/

clock_test.c

// Copyright © 2016 Martin Ueding <mu@martin-ueding.de>

// Test the cost of various time implementations.

#include <mpi.h>
#include <omp.h>

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void pretty_print(const double start,
                  const double stop,
                  const char *const method,
                  const long runs) {
    const double duration = (stop - start) / runs;
    printf("%20s: %g s\n", method, duration);
}

int main(int argc, char **argv) {
    MPI_Init(&argc, &argv);

    double start, stop;
    const long runs = 10000000;

    start = omp_get_wtime();
    for (long run = 0; run != runs; ++run) {
        MPI_Wtime();
    }
    stop = omp_get_wtime();
    pretty_print(start, stop, "MPI_Wtime", runs);

    start = omp_get_wtime();
    for (long run = 0; run != runs; ++run) {
        omp_get_wtime();
    }
    stop = omp_get_wtime();
    pretty_print(start, stop, "omp_get_wtime", runs);

    start = omp_get_wtime();
    for (long run = 0; run != runs; ++run) {
        clock();
    }
    stop = omp_get_wtime();
    pretty_print(start, stop, "clock", runs);

    start = omp_get_wtime();
    for (long run = 0; run != runs; ++run) {
    }
    stop = omp_get_wtime();
    pretty_print(start, stop, "none", runs);

    MPI_Finalize();

    return 0;
}